Electric heating apparatus



My 5, 1953 H. N. IPsEN ELECTRIC HEATING APPARATUS Filed Feb. 16, 1950 NvsNTQw-\ Q-(oLr-od Ipesem )f 5 TTORNSYM Patented May 5, 1953 UNITED STATES PAT-ENT OFFICE fEIiECTRIoJHEATINGARPARnTUS .-:HaroldrNaIpsem Rockford, Ill. -Applicatiourebruary 16, 1950;fsefialNofiugsas -4- Claims.

'a y'novel -manner With-respect Iso-each other'lto -minimize heating of the walls of thefurnace Vand the transmission of heat through the same,

Atnother object is 'to'formthe heater as' a tube A'of lceram-ic `Amaterial fwhich V'enclos'es `a vhigh re- --Slstanceelectric Yheating element and `Which `is mounted on 'the yfurnace Walls in `aA nvel'm'anner tdminirnize the' length of'thetube'and'the stresses thereon#during"thermal expansion and contrac- 'tiorrofthe tubeand the Walls-whereby to prevent "breakage'of'thetube Otherpbjects and Aa'dvautag'esI of the invention 'will 'become LAapparent from Vthe Yfollowing -de- Atailed description `taken` in `connectionwith the faccompanying drawings, in which l v Figure ,'1 vis a fragmentary verticalfsection 'of (heat t1"eating*apparatus4 involving the novel featuresof'the-present invention.

illg 2"is -a 'fragmentary enlargement of a part of rug. 11..

-3is'a'secton taken along -the`l'ine3-3 ornata Y Elin the drawings, the invention 4is "shown for 'purposes'df illustration' in a fr xrna-cemountedA on af'fraieIU and having aheating'chamber I'If'defined by top and bottom Walls I2 and I3', end Walls' f4, andspaced upright side Walls I5. A platform orziloor I6 Supported on the side Walls and spaced above'thebtt'oin vvall supports" workpieces (not Nshow'n) 'to be heated lWithin the chamber. Spanning thefsidev walls andiextending at opposite ends into alnediholes Ilttherein fatgpointsf-spaced along .the :chamber are one i, or .morezzelectric..heaters 'Lain ith'eiform ofr.tubes I B :of-.refractorymaterial Which'lenclose heating-ele sistance Wire such as Nichronle each connected at opposite ends to lead wires 2l `and embedded in a non-metallic refractory material 22 such as powdered magnesium oxide which is an electric insulator and has relatively high heat conductivity. The alined holes in this instance are circular in cross-section.

In accordance with the present invention, the heaters I8 are constructed and supported in the alined holes I'I in a novel manner to minimize heating of the side Walls I of the furnace or the transmission of heat therethrough and to reduce breakage of the tubes I 9. For this purpose, each tube is made substantially smaller in diameter than the holes and slightly longer than CII i or "the like 'having lower electrical resistance' l,so

that little heat. is v"generated Within 'the holes or ltheendfportons' of the tubes. With 'eac'h' heater `cfn'istiucted and arrangedin'the holesll inthls fmanner, they end portions 'of the' tube are heated only lindirectly '.by 'the high resistance "heating coiIZiI and, thereforefare' of a lower temperature `thanv the i intermediate 'portion 'of the tube so as to minimize heating 'of' the furnace Walls.

'lTo preventthe escape of heat from' the chamber through each "hole I'I,the "latteris reducedin size adjacent its outer end to receive only the 4leadwire 2I projecting from the end of the heater IS-re'stingonthe inner endoithehole. Inthis instance-such reduction ofthe size of each hole isf-efectedbyaninsulating plug "23 of suitable 'refractory `Inaterial pressed into the hole and vapertlr`ed' `as at u24 -to'receive'the'lead Wire 2|. Theaperture 24 is `slightly"larger rin diameter than y'the lead Wire `to prevent :the passage of heatlthro-ugh the aperture-While permitting the Wire to' vmove freely therein during axial expanv'sion and contraction of the tube.

Extending at'leastpartially around the/periph- A"ery of each 'of'thew'holesvl'lon the inner end thereof isa support Y2'5 Vpreferably of a-nonemetallic heat-resistantmaterial `Whickzh" is formed with a curved-'surface 26 thereon facing inwardly from the "defining surfaces ofjthe' hole to engage the "outer Yp"erir`rhery of the *tube 'end extending into the hole. In the present instance, the supports are in the form of rings pressed into the inner ends of the holes and having flanges 21 on their inner ends engaging the inner sides of the side Walls I5 around the holes. By locating the rings at the inner ends of the holes and curving the tube engaging surfaces 26 on the rings, the span of each tube is small resulting in correspondingly small lateral stresses therein. Also, each tube may expand and contract freely With none of the expansion and contraction stresses in the furnace Walls being transmitted to the tube. Thus, danger of breakage of the tubes is minimized.

It will be apparent that when an electric current is passed through one of the heaters I8 constructed and mounted as above described, only the intermediate portion thereof will be heated directly by the heating coil 20, the ends of the tube. and therefore the side walls l5, remaining relatively cool since the lead wire 2| has a low resistance and because the heating coil extends short of the tube ends. Since the tube extends short of the outer ends of the holes and the latter aresealed by the plugs 23, heat is prevented from escaping outwardly through the holes I1 from the chamber Il. Also. the tube is free to expand and contract freely relative to the furnace walls without danger of breakage owing to the size of the holes and the presence of the support rings 25.

I claim as mv invention:

1. Heat treating apparatus having, in combination. means dening a chamber to be heated and including laterally spaced upright walls having n alined holes extending therethrough, apertured insulating plugs pressed into said holes on the outer ends thereof. supports of non-metallic heatresistant material extending at least partially around the peripheries voi. said holes on the inner ends thereof and having curved surfaces thereon facing inwardly from the defining surfaces of the holes, a tube of refractory heat-resistant' material substantially smaller in external dimension than said holes, said tube spanning said walls and extending into said holes short of said plugs to rest adjacent opposite ends on said curved support surfaces whereby to 'permit free expansion and contraction of the tube, a non-metallic refractory powder filling a portion of said tube intermediate the ends thereof, and an electrical resistance heating element embedded in said powder with the end portions extending slidably out through the apertures in said plugs and providing terminals disposed outside of said chamber.

2. Heat treating apparatus having, in combination, means defining a chamber to be heated and including laterally spaced uprightv walls, means on said walls defining alined holes extending therethrough, apertured insulating plugs pressed into said holes on the outer ends thereof, a tube of refractory heat-resistant material smaller in external dimension than said holes, said tube spanning said Walls and extending into said holes short of said plugs to rest slidably on the dening surfaces of the holes and permit free expansion and contraction of the tube during heating and cooling thereof, a non-metallic refractory powder filling a portion of said tube intermediate the ends thereof, an electrical resistance heating element embeddedl in said powder and extending along said tube short of the ends thereof and short of said chambervwalls, and electrical conductors of low resistance connected to opposite ends of said resistance element and extending from pointsrwithin said tube '4 and said chamber slidably through the apertures in said plugs.

3. Heat treating apparatus having, in combination, means dening a chamber to be heated and including laterally spaced upright walls, means on said walls defining alined holes extending therethrough, a tube of refractory heat-resistant material smaller in external dimension than said holes, said tube spanning said walls and extending into said holes short ofthe outer ends thereof to rest slidably on the defining surfaces of the holes and permit free expansion and contraction of the tube during heating and cooling of the same, a non-metallic refractory powder filling said tube between said chamber walls, and electrical resistance heating element embedded in said powder and extending along said tube short of the ends thereof and short of said chamber Walls, and conductors of low electrical resistance connected to opposite ends of said resistance ele- -ment and extending from points Within said tube and said chamber through said holes to provide terminals disposed outside of said chamber, the outer ends of said holes being reduced in size to receive said conductors slidably and prevent the escape of heat from the chamberA through the holes. n

4. Heat treating apparatus having, in combination, means deining a-chamber to be heated and including laterally vspaced upright walls,` means on said walls dening alined holes opening inwardly into said chamber, means contacting and Iixedto said walls and closing the outer ends-of said holes, a tube of refractory heat-resistant material of a size substantially smaller in'external dimension than said holes and spanning said walls with the` ends thereof projecting into and supported Within said holes, at least one of said ends extending into its associated hole short of the closing means and resting loosely on the dening surface of said hole to permit` free longitudinal expansion and contraction of the tube by movement of said one tube end toward and away from said closing means, an electrical resistance heating element disposed within said-tube intermediate the ends thereof, said closing means having an aperture substantially smaller in size than said tube, and a lead wire extending through said apertureV and connected to said resistance heat-4 ing element. y f

l a HAROLD N. IPsEN.

'References cited in the me of this patentr UNITED STATES PATENTSv Number Name Date Re. 18,420 Shaw Apr. 12, 1932 1,367,341 Abbott Feb. 1, 1921 1,555,292 Keene Sept. 29, 1925 1,903,036 Francis Mar. 28, 1933 2,491,579 Poland Dec. 20, 1949 

